Bit balling treatment

ABSTRACT

A solid body contains a surfactant and crushed walnut hulls. The solid body is shaped to predetermined dimensions that permit passage through the central interior opening of drill pipe. The solid body dissolves in drilling mud for delivery of a pill to the annulus through the drill bit nozzles. The pill is an effective treatment against bit balling.

BACKGROUND

1. Field of the Invention

The field of the invention pertains to drilling fluid additives that maybe used to remediate bit balling that otherwise occurs in clay and shale(hereafter referred to collectively as ‘clay’) zones as a well isdrilled.

2. Description of the Related Art

Water-based drilling mud systems are usually employed during thedrilling of a well, such as an oil or gas well. The well bore maypenetrate a clay zone, and this circumstance exposes naturally occurringclay minerals. Water in the mud is able to hydrate the clay minerals,which then typically swell to cause a number of known problems.

The clay problems may be addressed by using chemical treating agents.This is done using salts and/or polymers in the drilling mud. Salts,such as KCl or CaCl, reduce the clay swelling and dispersion. Suchpolymers as partially hydrolyzed polyacrylamide are sometimes added tothe drilling mud used to encapsulate the clay, thus keeping the clayfrom hydrating and swelling. Alternatively, oil-based mud may be used toprevent the swelling phenomenon, but since oil mud also contains water,it is necessary that the salinity of the water be sufficiently high toprevent water from entering the clay by osmosis.

Bit balling is one problem that is frequently encountered when drillingthrough clay. The problem is caused by the tendency of hydrated clayminerals to stick or adhere to the bit and bottom-hole assembly of adrill string. Although this problem may also occur in oil based mud, itis relatively rare as compared to water-based mud. From an operationsstandpoint, bit balling is evidenced by increased pump pressures as theflow pathway through the well bore annulus becomes blocked, reducedrates of penetration, blocked shaker screens, a required over-pulltension that occurs due to a restricted annulus when tripping pipe, andpossible stuck pipe.

Once bit balling is diagnosed, conventional methods of remediation areto increase the weight on the bit, add chemicals and perhaps pull thedrill pipe out of the hole to clean the bit and bottom hole assembly.For a water-based mud, a detergent may be added to the drilling mud toreduce the ability of the hydrated clay to stick to the bit and bottomhole assembly. Glycol may also be added at about 3% to 4% of systemvolume. This often fails to cure the problem.

Preventative measures against bit balling include the review of priordrilling reports to ascertain and adopt procedures that have previouslyworked in the geographic area to overcome bit balling. A KCl/polymer orCaCl/polymer mud may be used to inhibit the swelling of clays. Theselection of a bit may also affect bit balling, where it is known thatpolycrystalline diamond compact bits are more prone to balling than aretri-cone bits, and it is further the case that the arrangement of teethstructures on tri-cone bits may affect bit balling. This is shown forexample, in U.S. Pat. No. 4,984,643 issued to Isbell et al.

Another way to address the problem of bit balling is to optimize the mudsystem hydraulics. This may be done for either large or small bore bits.In addition to sizing the nozzles for optimum delivery of hydraulichorsepower, it is also possible to direct the nozzle discharge tooptimize bottom-hole cleaning in a ‘mud pick’ configuration. This isreported, for example, in Smith et al., Hydraulics Optimization Researchin Large Diameter Bits Reduces Operator's Variable Costs,AASDE-05-NTCE-58 (2005).

It has also been reported that maintaining a negative potential of a fewvolts on the drill string assembly may liberate water at the interfacebetween the bit and the hydrated clay. See Sanjit et al., The effect ofelectro-osmosis on the indentation of clays, Proceedings of the 32nd USRock Mechanics Symposium, Norman Okla. (July 1991).

Although the art does provide remedial measures, bit balling continuesto be a significant factor affecting the costs of drilling new wells. Itis particularly difficult to pump pills of material to remediate theproblem of bit balling, and any such measures often provide onlytemporary relief.

SUMMARY

The present instrumentalities overcome the problems outlined above andadvances the art by providing a compact and easy to use article ofmanufacture for introducing treatments to a drilling mud system.

In one embodiment, the article is formed as a solid body that contains acombination of nut hulls and a surfactant that are bound together withan optional carrier. As used herein the term “solid” also encompasses agel unless specifically noted otherwise. The carrier may be a soft wax,such as beeswax, having a melting temperature much less than is expectedat the bit. Beeswax generally melts at a temperature of 144° to 149° F.Thus, in an area where there exists a geothermal gradient of 1.8° F. per100 feet of well, it may be expected that a well in excess of 8000 feetof depth will reach this temperature. A plasticizer, such as glycerol orcastor oil, may be added to reduce the melting temperature.Alternatively, a water soluble polymer may be used as the carrier. Thismay be, for example, an ethylene/vinyl alcohol copolymer with ade-structured starch composition and a plasticizer, such as glycerin,with urea as a de-structuring agent. Suitable compositions are reportedin EP0400532A1 to Bastioli et al., which is incorporated by reference tothe same extent as though fully disclosed herein. The carrier isnonessential, since the surfactant itself may bind the nut hulls.

In dissolved form, the solid body forms a pill. A “pill” is herebydefined as any relatively small quantity, less than 200 bbl, of aspecial drilling fluid that is provided to accomplish a specific taskthat the regular drilling fluid cannot perform. Examples of conventionalpills include the use of high-viscosity pills to help lift cuttings outof a vertical well bore, pipe-freeing pills to destroy filter cake andrelieve differential sticking forces and lost circulation material pillsto plug a thief zone. The pill that is formed of the dissolved solidbody is used against bit balling.

The surfactant may be any surfactant; which may be a detergent, awetting agent, or an emulsifier. Detergents are preferred. The detergentmay be a soap, such as a sodium soap of a fatty acid. The detergent mayalso be classified as an ionic, anionic, or cationic detergent dependingupon the mode of action. Sulfonates are especially preferred, andparticularly linear alkyl sulfonates for their biodegradability. Soapsmay be particularly useful, as a saponification reaction may be used toreact and harden a glycerol ester as a soap during the casting process.In some embodiments, a potassium or sodium lye may be used to saponify aC15 to C20 fatty acid. The C18 fatty acids are particularly preferredwhere, for example, the resultant soap may be a saponified castor oilcomprised mostly of ricinoleic acid, or oleic acid.

The nut hulls may be any nut hulls, but the use of walnut hulls isparticularly preferred. Crushed walnut hulls that have been screenedthrough −30/+60 US mesh are commonly purchased on commercial order andused to remediate lost circulation in wells. These may be mixed withother hull materials, including similarly sized cottonseed hulls, pecanshells, and almond shells. Use of the walnut hulls in the presentinstrumentality differs in that the walnut hulls are generally hard andlightweight, and may be used to blast hydrated clay from the bit andbottom hole assembly, once softened by the surfactant.

The article of manufacture may be used in a method of treating adrilling mud system to overcome bit balling

The following disclosure makes these and other advantages are apparentto those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a solid body that may be used to provide a pill for thetreatment of bit balling;

FIG. 2 is a cross-sectional view taken along line 2-2′ of FIG. 1;

FIG. 3 shows another embodiment of the solid body;

FIG. 4 shows the solid body being inserted into a drill string;

FIG. 5 is a top view of the solid body inserted into the drill string;

FIG. 6 shows an improvement in a rate of penetration obtained form useof a pill that contains a combination of a detergent and crushed nuthulls;

FIG. 7 shows a system for molding the solid body; and

FIG. 8 provides additional detail for the molding system of FIG. 7;

DETAILED DESCRIPTION

There will now be shown and described an article for use in treating abit balling problem. FIG. 1 shows an article 100 that is formed as agenerally cylindrical tube having a diameter D and a length L. A centerhole 102 presents a diameter D′. A wall 104 is made of a surfactant,crushed hulls, and a dissoluble carrier. FIG. 2 presents a sectionalview taken along line 2-2′ of FIG. 1.

Dimensions are not critical, except the diameter D must be sufficientlysmall to pass through the interior of a drill pipe. Hole 102 is providedto assist circulation of mud through the article 100, in order tofacilitate dissolution. By way of example, suitable dimensions for mostapplications include a diameter D of 1 to 1.5 inches, a length L ofabout 20 to 30 inches, with 27 inches being most preferred, and adiameter D′ of about 1/16 to ½ inch.

Article 100 contains a combination of nut hulls and a surfactant thatare bound together with a carrier. The carrier may be a soft wax, suchas beeswax, having a melting temperature much less than is expected atthe bit. Beeswax generally melts at a temperature of 144° to 149° F.Thus, in an area where there exists a geothemal gradient of 1.8° F. per100 feet of well bore, it may be expected that a well in excess of 8000feet of depth will reach this temperature. A plasticizer, such asglycerol, may be added to reduce the melting temperature suitably forshallower depths. Alternatively, a water soluble polymer may be used asthe carrier. This may be, for example, an ethylene/vinyl alcoholcopolymer with a de-structured starch composition and a plasticizer,such as glycerin. Urea may be used as a de-structuring agent. Suitablepolymeric compositions for this use are reported in EP0400532A1 toBastioli et al.

In some cases, the carrier may be a soap. It is possible to combine thenut hulls with the glycerol ester of a fatty acid, or another ester,pour the mixture into a mold, and cast the article 100 to saponify andharden the mixture, then release from the mold. In this case, theresultant soap holds together the nut hulls.

FIG. 3 shows another embodiment as article 300 with center hole 302. Inthis case, half of the article 300 is a surfactant 304 and the otherhalf 306 contains nut hulls bound with a carrier, as described above incontext of the wall 104 that is shown in FIG. 1. The respective halves304, 306 are cast together in a common mold.

FIG. 4 shows article 100 in use. Drill pipe 400 is retained by slips 402in a rotary table 404. The drill string, as represented by drill pipe400, is broken to make a new connection. Tongs 406 are in position foruse in assembling the next connection, as is required to advance thedrill pipe 400 down the well-bore as the well is drilled. The article100 is being placed into a female joint 408 that will receive a male pinof the next piece of drill pipe (not shown) as the connection proceeds.Any number of articles 100 may be manually placed in the drill pipe 400in this manner.

FIG. 5 shows the article 100 positioned in the female joint 408. Athreaded surface 500 transitions to a curved wall 502 and conduit 504.Article 100 resides within conduit 504. From this position, theconnection may be assembled with joint 408, and active drilling mayrecommence. The recommencement of drilling necessarily entails thepumping of mud through conduit 504. The mud drives article 100 down holetowards the bit. As article 100 proceeds down hole the water in the mudand/or temperature of the mud tends to dissolve article 100 to releasethe surfactant and the nut hulls, providing what is known in the art asa ‘pill’. The surfactant and the nut hulls pass through the nozzles of adrilling bit and enter the annulus of the well-bore where they workagainst bit balling. The hole 102 and the space between article 100 andthe walls of conduit 504 assures that mud pumped through conduit 504 isable to bypass article 100, in order that article does not fullyobstruct conduit 504 if article 100 has not completely dissolved by thetime it reaches the drill bit (not shown) at the bottom of the hole.

FIG. 6 shows an improvement in rate of penetration that was obtainedusing a pill of this nature where the pill contained 0.1 gallons ofcrushed walnut hulls and 0.3 gallons of liquid soap. The “after”penetration rate shows comparatively that a bit balling problem has beenovercome.

FIG. 7 shows a system 700 that may be used to make article 100. Aninjection system 702 disburses liquid material through line 704 into tomold system 706. A nut hull hopper 708 provides nut hull material forcombination with the liquid in the mold system 706. The injection system702 may be, for example, a screw extruder system for the liquefaction ofwater soluble polymer material, as described above in context ofEP0400532A1. The injection system 702 may also be a metering system forpumping a soap precursor that may be saponified in the mold system 706.Initially cast with a liquid, the articles 100, 300 harden in the moldsystem 706.

FIG. 8 provides additional detail with respect to one embodiment of themold system 706. A bivalve mold 800 is formed of respective halves 802,804, which are notched as at 806, 808 to accommodate line 704. Uponopening of the mold 800, a robotic arm 810 imparts motion 812, 814 toswing the halves 802, 804 away from line 704. With the mold 800 removedin this way, a pneumatic cylinder 816 is mounted on line 704, and iscapable of extending head 818 in direction 820 to release cast articles100 from line 704. The arm 810 then positions the mold 800 as shown inFIG. 8 for receipt of nut material from nut hopper 708 (not shown inFIG. 8). With the mold 800 subsequently closed, line 704 receives liquidmaterial from the injection system 702 and disburses the same into moldcavity 822 through perforations 824. The mold halves 802, 804 may beconfigured with a heating structure, such as resistive electrical coilsor a water jacket (not shown) to heat materials in the mold, forexample, to perform a saponification reaction.

EXAMPLES

Table 1 provides various formulations of materials that may be used asarticles 100 or 300: A 1.5″ diameter stick that is 27″ long contains0.27 gallons of material. Although this is less than the total of 0.4gallons used in actual testing reported herein. two or more sticks maybe used at one time in a stacked sequential order. The calculationsbelow are based on a total stick volume of 0.27 gallons.

TABLE 1 Example compositions Article Material Amount Processing CommentsA Saponified Castor Oil 0.2 gal Heat to 115°. Mix .01 gal (SCO) Crushedwalnut 0.07 gal of the SCO together with hulls sized - the walnut hulls.Inject 30/+60 US mesh remainder of the SCO into one end of the mold andthe SCO/ Walnut hull mixture into the other end. Cool for 360 minutes.Remove from mold. B Beeswax .01 gal Heat Beeswax to 144° and mix withwalnut hulls. Saponified Castor Oil 0.19 gal Heat SCO to 115°. Inject(SCO) Crushed walnut 0.07 gal each mixture into opposite hulls sized -ends of the mold. Cool for 30/+60 US mesh 360 minutes. Remove from mold.C Oleic Acid 0.14 gal Add Lye to water. Mix Lye 0.02 gal lye/watersolution into Crushed walnut hulls 0.07 gal Oleic Acid. Stir untilsized - thick. Mix .01 gal of this 30/+60 US mesh solution together withthe walnut hulls. Inject remainder of the solution into one end of themold and the Walnut hull mixture into the other end. Cool for 360minutes. Remove from mold. Water 0.04 gal

Those skilled in the art appreciate that the foregoing instrumentalitiesteach by way of example, and not by limitation. Accordingly, what isclaimed as the invention also encompasses insubstantial changes withrespect to what is claimed. The inventor hereby states his intention torely upon the Doctrine of Equivalents to protect the scope and spirit ofthe invention.

1. An article for use in the treatment of drilling mud, comprising: asolid body including a surfactant and nut hulls bound, the body formedto have predetermined dimensions permitting passage of the body throughthe interior opening of drill pipe, the surfactant being dissoluble indrilling mud.
 2. The article of claim 1, wherein the surfactant includesa detergent.
 3. The article of claim 2, wherein the detergent includessoap.
 4. The article of claim 2, wherein the detergent includes anon-ionic detergent.
 5. The article of claim 1, wherein the surfactantincludes a linear alkyl sulfonate.
 6. The article of claim 1, furthercomprising a plasticizer mixed with the surfactant.
 7. The article ofclaim 6, wherein the plasticizer includes glycerin.
 8. The article ofclaim 6, wherein the plasticizer includes a glycol.
 9. The article ofclaim 1, wherein the nut hulls include crushed walnut hulls.
 10. Thearticle of claim 1 retained within drill pipe.
 11. The article of claim1, further comprising a carrier used as a binder for at least one of thesurfactant and the nut hulls.
 12. The article of claim 11, wherein thebinder includes a water soluble polymer.
 13. The article of claim 11,wherein the binder includes beeswax.
 14. A method of drilling comprisingthe steps of: providing a solid body formed of a surfactant and nuthulls, the solid body formed to have predetermined dimensions thatpermit passage of the solid body through the interior opening of drillpipe, and the surfactant being dissoluble in drilling mud; breaking adrill string to make a connection; introducing the solid body into theinterior of the drill pipe; completing the connection; and recommencingdrilling operations with the pumping of mud to dissolve the solid bodyin the mud and form a pill for action against bit balling.